Calling it "the most advanced mobile operating system in the world," Steve Jobs announced at WWDC 10 today that the next revision of iPhone OS will be called "iOS 4." With a new name that reflects the spread of the operating system from the iPhone to the iPod touch and now the iPad, iOS 4 went Gold Master today with what Jobs said were 1,500 new features. The upgrade will be available for the iPhone 3G, 3GS, and the iPod touch on June 21 - free for the first time to iPod touch owners - and will be preloaded on the iPhone 4 when it ships three days later.

The marquee feature of the new OS remains multitasking, and Steve Jobs showed off Pandora streaming in the background as he checked his mail during the keynote address. Mail now has a unified inbox for multiple services, as well as the ability to show sequential messages with the same subject line as threads. Apps can now be organized into folders, which can be moved, renamed, or kept in the Dock. In a first for the iPhone, Microsoft Bing is now a search option along with Google and Yahoo, though Google remains the default - for now.

Jobs also spent a fair amount of time highlighting the new iAds mobile advertising network that Apple is launching with iOS 4. iAds, Jobs explained, combines "the emotion of TV with the interactivity of the web" and will let users "explore ads" (really?) without being hijacked out of their favorite apps."

iOS 4 will not be available for the first-generation iPod touch. And though it can run on the 3G, it will not support multitasking.